The present invention relates to inspection of parts and, more particularly, to quality control inspection of circular parts. Heretofore, quality control of circular parts, such as seals, diaphragms, wiring protection through holes, and the like, has been difficult and tedious. Parts that fall into this category typically include, but are not limited to, transmission seals, grommets, actuator diaphragms and the like. These products may be metal, coated metal, plastic or polymeric materials, composite materials and the like, or a combination thereof.
Conventional inspection methods are typically manual and are, consequently, labor intensive. Human inspectors look at each part individually and visually locate cosmetic, Material or other defects. This process is subject to fatigue and inattentiveness, and so is unreliable and inconsistent. In the automotive industry, quality standards are increasingly demanding and consequently make increasing demands on quality control departments of suppliers. The inability of human inspectors to reach the high production levels while maintaining the levels of quality required by discerning customers, such as automotive companies, coupled with the repetitive motion injuries frequently sustained in such operations, make automated inspection more a requirement than an option.
The problem the suppliers face is a lack of devices capable of inspecting for defects that humans can, in fact, find. Duplication of human inspection is difficult. Even machine vision systems using ordinary camera and computer technology find it hard to detect these defects since cameras look only at the two-dimensional projections of these defects.
Even with ordinary machine vision and other methods, manufacturers are dissatisfied with many automated inspection approaches and seek alternatives to what is commercially available. Two-dimensional (2-D) machine vision is one of the more advanced means of inspection. But, as noted above, even this is thought by some manufacturers to be inadequate. The rationale is that cosmetic and other types of defects can be detected by 2-D machine vision only if the defect reflects light differently from the surrounding material. This is difficult to assure. While three-dimensional (3-D) methods have been developed, current three-dimensional methods are regarded as slow. Although the newly developed three-dimensional methods appear to offer high resolution, inspection times are considerably longer than the one part per second or two part per second that manufacturers want.
Consequently, new tools are needed to approach the level of inspection that can be achieved using human inspectors, while maintaining high levels of reliability and consistency. Furthermore, it would be highly desirable for the method and apparatus using three-dimensional methods to inspect parts at a rate of one to two parts per second. In addition, in order for the method or apparatus to be fully utilized, the method and apparatus needs to be easy for manufacturing engineers to inspect a variety of parts that include preprogram inspection parameters. In addition, ideally the system should not permit operators to change program inspection parameters; instead, operators should only be able to call up a part number and have all the associated parameters loaded automatically.
According to the present invention, an inspection system includes hardware and software to inspect both sides of circular objects and, preferably, inspect both sides of circular objects at rates approaching one part per second. Such parts that can be inspected using the system of the present invention include grommets, diaphragms, rotary seals, and the like.
According to one form of the invention, the inspection system includes a camera, a computer which is in communication with the camera, and a light source. The light source is energized in order to project light onto a part which is to be inspected and viewed by the camera. The camera generates profile signals in response to the light on the part. The computer, which receives the profile signals from the camera, is preprogrammed to gather the profile signal data and analyze the profile signal data by comparison to known good part data. In this manner, by comparing the data from the inspected part to the known good part data, the system can detect defects in the part.
In one aspect, the structured lighting light source generates a structured light, for example, a line light. In the preferred form, the light source comprises a laser line generator. Preferably, the line light is projected down onto the part while the camera views the line light offset at an angle, for example, an angle in a range of approximately 30-60xc2x0 from the line light.
In another aspect of the invention, the inspection system includes a second light source and a second camera. The second light source directs light onto a second side of the part. The second camera generates profile signals for the second side of the part, which are similarly analyzed by the computer. In the further form, the inspection system includes a second computer, such that each computer is associated with a camera, preferably with the first and second computers being networked. In preferred form, the cameras comprise high speed cameras, such as analog or digital cameras. Further, the high-speed camera may include addressable or non-addressable configurations. These camera forms are known to those skilled in the art of machine vision.
In other forms, the structured lighting light source may generate single or multiple lines or other geometries of projected structure light, including, for example, dots, radial lines, chevron lines, circles, rectangles, general polygons and other methods.
In further forms, the part to be inspected is placed on a first conveyor which moves the part to be inspected into a first inspection position for illumination by the first light source. After inspection, the first conveyor preferably delivers the part to a second conveyor, with the part rotated or flipped so as to be viewed on a second side or surface, which moves the part into a second inspection region under the second light source for inspection by the second camera.
In one preferred form, the conveyor includes a belt with a minimum light reflectivity in order to minimize the secondary light reflections from the belt.
In order to track the position of the part on the conveyors, each conveyor preferably includes an encoder, which is coupled to and in communication with the computer. The encoders generate periodic pulses as the conveyors move. Each pulse generated by the encoder represents a fixed distance of movement of the respective conveyor.
In other forms, to reduce data acquisition time and analysis time, a sensor which is in communication with the computer, is positioned at or near the respective inspection locations on the conveyors. When a sensor detects a part, the sensor generates a signal to the computer which initiates the data acquisition and analysis process. For example, the sensor may comprise a fiber-optic-through-beam sensor. The fiber-optic-through-beam sensor generates a beam that preferably extends across the conveyor. When the beam is interrupted, the sensor generates a signal which signal triggers the computer software program to initiate the acquisition and analysis sequence. Preferably, the software is programmed to sample a preselected number of signals from the camera following the trigger of the sensor. In this manner, the number of blank lines or invalid readings are reduced.
In preferred forms, the cameras are positioned to have the same general orientation with respect to the structured lighting light source. In this manner, both sides of the part are inspected, one at each station. By viewing the parts from opposite sides but at approximately the same elevation angle, the shadowing effects experienced by the cameras are negated and, together, the cameras view the entire part.
Each of the cameras views the laser line at an angle. Those skilled in the art of using structured light will recognize that some portions of some profiles of a part may be obscured by the part itself, owing to this angle of view. In these cases, a second camera viewing the part from the opposite side of the light line may be able to view the profile without this shadowing effect. Then the profiles can be combined and the effects of shadowing reduced or eliminated. In cases where surfaces of parts show little or no shadowing, such as diaphragms, there may be no advantage to this method while in other cases, such as rotary seals, this method may be helpful.
In yet another aspect of the invention, the inspection system includes a pair of 2-D cameras, which can be used to inspect a part, either before or after the 3-D inspection stations. In this manner, the 2-D cameras may provide another check for lateral dimensional conformity and may provide better inspection of parts that have deep or narrow structures, such as sidewalls.
In further forms, the inspection system includes a removal mechanism when a defective part is detected. Removal can be initiated at the camera or at some other location. In which case, in order to track a defective part, the system may include, for example, a shift register. When the software determines that a part is defective, the software sets a xe2x80x9cdefective bitxe2x80x9d in the shift register. As the conveyor moves, the shift register moves this xe2x80x9cdefective bitxe2x80x9d along to the next bit after some number of counts from the encoder. In this manner, the time between inspection and removal can be adjusted. Optionally, the period between detection of a defective part and removal may be selected by the user.